Plastic materials have advantages such as low cost, light weight, and excellent processability, and are therefore widely used in various fields such as consumer electric products, automotive materials, and building materials. Plastic materials having excellent transparency, heat resistance, and mechanical properties are also used as optical films or plates (hereinafter, they are together abbreviated to ‘optical sheets’) used in liquid crystal displays or projection televisions, which are fields that have been growing recently.
However, since plastic materials have the defect that the surface is easily damaged, if this defect becomes an issue in terms of the application or the production process, it becomes necessary to carry out a hard coat treatment for protecting the plastic surface.
As a hard coat material, an active energy beam-curable composition is widely used since it has not only excellent scratch resistance, etc. but it also has excellent productivity due to energy conservation and a high cure rate. As an active energy beam-curable composition, an acrylic composition comprising a polyfunctional (meth)acrylate as a main component is predominant and has the advantage that it is inexpensive and has excellent scratch resistance.
However, polyfunctional (meth)acrylates have the problem of warp due to large curing shrinkage and the problem of swarf being generated when cutting a sheet.
In particular, swarf is not desirable in an optical sheet production site where a degree of cleanness is required. Furthermore, when used outdoors, there is the problem that cracks are easily caused on the surface due to exposure to ultraviolet light (UV).
As a technique for suppressing warp while giving excellent scratch resistance, an active energy beam-curable composition comprising an ethylenically unsaturated compound (A) having an isocyanurate skeleton, organic-covered inorganic microparticles (B) obtained by a condensation reaction of inorganic microparticles (b1) and an organic silane compound hydrolysis product (b2), a photopolymerization initiator (C), and a solvent (D) has been reported (Patent Document 1).
Furthermore, as a technique for satisfying both scratch resistance and weather resistance, an active energy beam-curable composition comprising (A) an alkoxysilyl group- and (meth)acryloyl group-containing resin, (B) colloidal silica having primary particle size of 1 to 200 nm, (C) a UV absorber, and/or (D) a light stabilizer has been reported (Patent Document 2).
Recently, as a composition for hard coat application that does not contain inorganic microparticles and has excellent scratch resistance and little warp, an active energy beam-curable composition comprising a penta- and/or hexa-acrylate of dipentaerythritol, an acrylate of pentaerythritol trimer to heptamer, and an acrylate of pentaerythritol octa- and higher-multimers at a predetermined ratio, and further comprising a photopolymerization initiator and a polyether-modified organopolysiloxane has been reported (Patent Document 3).
When the active energy beam is light there is, as a general problem with photocurable compositions, a problem with odor, etc. due to a decomposition product of a photopolymerization initiator. As a technique for solving this problem an active energy beam-curable composition comprising a polyfunctional maleimide compound that can be photocured without the addition of a photopolymerization initiator or with the addition of a small amount thereof has been reported (Patent Documents 4 and 5).    Patent Document 1 JP-A-2006-225434 (JP-A denotes a Japanese unexamined patent application publication)    Patent Document 2 JP-A-2004-346228    Patent Document 3 JP-A-2007-231138    Patent Document 4 JP-A-11-124403    Patent Document 5 JP-A-2005-23101